1. Field of the Invention
There are many types of liquid level gauges. When the gauge is required to determine the level in a closed container most gauges are constructed in a manner to require a dynamic seal to prevent loss of product in the tank. The effectiveness of a seal is important when the tank contains pressurized liquid. In many cases the liquid is under pressure of up to 600 psig.
2. Description of the Prior Art
Most of the liquid level gauges used to detect the liquid-vapor interface in a closed tank utilizes a float that, when moved, moves a cable extending through the top of the tank. Such construction requires a dynamic seal.
There is one known device for measuring liquid level that requires only a static seal. That device is disclosed in U.S. Pat. No. 2,371,511. In the device of that patent there is a light magnet mounted on a float in the tank. A vertical magnetized shaft extends upwardly through the float that has its magnet with magnetic pole faces. Rotation of the float is prevented. As a result, the shaft rotates when the float moves vertically. At the upper end of the shaft within the tank is fixedly mounted a permanent bar magnet. This magnet is within a cylindrical vertical offset in a part of the top wall of the tank. A central upstanding boss on the offset rotatably supports a vertical stub shaft on the top end of which is fixedly mounted a pointer. On the stub shaft is fixedly mounted an inverted cylindrical cup that supports a ring magnet at the elevation of the permanent bar magnet mounted on the magnetized bar in the tank. The bar magnet and the ring magnet constitute a synchronous radial type of magnetic drive so that the turning of the vertical shaft in the tank by the vertical movement of the magnet on the float turns the ring magnet and thereby turns the pointer. By virtue of this construction the pointer will indicate the position of the float, that is indicative of the position of the liquid-vapor interface in the tank.